The invention relates to pipettes for taking liquid samples.
A sampling pipette is known, e.g. from document FR-2 696 110, that is suitable for receiving a discardable cone at its bottom end, which cone is held on the pipette by means of friction. The pipette has an ejector that can be actuated by means of a button adjacent to a sampling button. Pressing on that button enables the cone to be pushed away from the pipette when it is desired to replace a used cone with a new cone.
In that pipette, the ejector has an arm with a bottom portion for coming into direct contact with the cone, and a top portion to which the bottom portion is secured by friction engagement in the longitudinal direction of the pipette. This engagement enables the bottom portion of the ejector to be assembled simply and quickly onto the pipette and to be removed with the same advantages. Nevertheless, while ejecting a cone, at the moment when the cone gives way and becomes detached from the tip of the pipette, the ejector follows the cone and its speed increases suddenly. The movement of the ejector is then stopped sharply because the top portion comes into abutment against the body of the pipette. The same braking force is transmitted to the bottom portion via the friction engagement. Unfortunately, this force tends to undo the engagement between the bottom and top portions and to separate them from each other. After ejecting some number of cones, it can thus happen that the bottom portion of the ejector becomes separated from the pipette in untimely manner.
Document WO 96/37302 has a FIG. 19 providing for an ejector in which the bottom portion that pushes against the cone is itself engaged in the longitudinal direction of the pipette in a top portion of the ejector. A fixing tongue holds together the two interconnected portions and prevents them from separating in untimely manner. Nevertheless, in order to remove the bottom portion, it is necessary to reach the tongue, and that is rather awkward.